Photochromic Polymer Films Research Articles

Dynamic color‐tunable ultra‐long room temperature phosphorescence polymers with photo‐chromism and water‐stimuli response for multilevel anti‐counterfeiting

AbstractDeveloping dynamic color‐tunable ultra‐long room temperature phosphorescence (URTP) polymers with afterglow of over 1 s, photo‐chromism, and multi‐stimuli response for practical anti‐counterfeiting and information security applications is attractive but very challenging. Herein, by doping multicolor phosphorescence pyridinium bromide L block or viologen‐based photo‐chromic V block into polyvinyl alcohol matrixes, the water‐stimuli‐responsive color‐tunable URTP polymer films with afterglow of up to 8 s and the reversible viologen‐based photochromic polymer films have been developed. More significantly, a series of dynamic color‐tunable URTP polymer films with ultra‐long afterglow of over 6 s, photo‐chromism, and water‐stimuli response have been successfully exploited by integrating L and V blocks into one polymer system. Mechanistic investigations have revealed that their photo‐chromism mainly comes from the photo‐generated viologen free radicals. Furthermore, their dynamic multilevel anti‐counterfeiting applications have been demonstrated. These results pave the way to develop smarter multifunctional URTP materials for anti‐counterfeiting and optical sensing.

Combining Photomodulation and Rectification in Coordination Molecular Wires Based on Dithienylethene Molecular Junctions

Thin films of photochromic coordination polymers deposited by layer-by-layer technique, based on iron (II) bis-terpyridine-appended dithienylethene blocks, were used to create light-switchable molecular junctions with high rectification ratios. These multilayer films show a modulation of the attenuation factor when exposed to light irradiation

A spectral-kinetic investigation of the negative photochromism of systems based on complexes of spiropyrans with metal ions

A comparative spectral-kinetic study of the negative photochromism of complexes of molecules of nitrosubstituted indoline spiropyrans with metal ions in solutions and polymer matrices is carried out. The possibility of creating polymer coatings with negative photochromism, based on the complexes of spiropyran molecules with metal ions is shown for the first time. It is determined that the efficiency of photochromic transformations of complexes depends on the nature of the polymer binder, the component composition of the polymer film, and the properties of metal cations. During the storage of photochromic polymer films in the dark, a spectral manifestation of the transformation of metal complexes into putative protonated complexes is revealed. It is found that the stability of the complexes is determined by the nature of the polymer binder and the affinity of the metal cations to an electron.

Fast photochromism in polymer matrix with plasticizer and real-time dynamic holographic properties

We have developed a photochromic polymer film for the use of real-time dynamic hologram, fabricated by the plasticized polymer doped with the fast photochromic molecule. The addition of a plasticizer into the conventional polymer is proved to be effective to improve the photochromic performances for the polymer film doped with the fast photochromic molecule that shows instantaneous coloration upon exposure to UV light and rapid fading in the dark. The plasticized photochromic polymers enable the real-time control of the writing and erasing of a holographic grating and show a higher recording sensitivity compared with other organic holographic materials.

The high stability of merocyanine and significant slow fading speed of naphthopyran in layer-by-layer assembled films via hydrogen bonding

A photochromic polymer film has been fabricated by the layer-by-layer (LBL) self-assembly through alternating the deposition of poly(acrylic acid) bearing a naphthopyran copolymer and poly(4-vinylpyridine) in an organic solvent. The multilayer assembly process is monitored via UV-vis spectroscopy by measuring the increase in absorbance at 380 nm, and the results reveal that the multilayer films grow in a uniform way in each deposition. Atomic force microscopy (AFM) images prove that the surface of the film was relatively smooth. The photochromic properties of the naphthopyran in the LBL films are investigated and the kinetic results confirm that the colored merocyanine in the LBL films show a significant slow fading speed (critical T1/2 decoloration time increased to 64 min in the 3-bilayer film) and are more stable than those in previous reports.

A real-time dynamic holographic material using a fast photochromic molecule

We have developed a real-time, dynamic holographic material that exhibits rapid colouration upon irradiation with UV light and successive fast thermal bleaching within tens of milliseconds at room temperature. Photochromic polymer films were prepared by a simple solution-casting method from the benzene solution of the mixture of the photochromic molecule, poly(ethyl acrylate), and poly(phenoxyethyl acrylate). The real-time control of holographic images using the photochromic polymer film yields a speed equivalent to the time resolution of the human eye. This new type of dynamic holographic material based on fast photochromism opens up an exciting new area of research in the future development of a large dynamic 3D display.

Photo-actuated bending of chromatic liquid crystal polymer strips and laminates

Photochromic liquid crystal polymer (LCP) films can undergo spontaneous mechanical deformations upon light illuminations. The light-induced strain is due to photoisomerization and the nematic–isotropic phase transition. A gradient strain exists due to absorption decay of the light intensity and will produce bending of LCP strips. Beam bending models are studied for single layered and bilayered LCP strips with substrate. The results show that the multilayered structures can have much larger bending curvature due to the utilization of the average light-induced contractions which were mostly not active for single-layered LCPs. Some structural optimizations for bilayered laminate are also discussed.

Photochromic fulgimide-containing silicones immobilized on the surface of polyarylate

Photochromic coatings immobilized on the surface of polyarylate films are prepared on the basis of fulgimides, oligosiloxanes, and oligosilazanes. The irradiation of coatings with UV light at a wavelength of @380 nm and visible light at a wavelength above 500 nm results in photoinduced reversible transitions between open and colored cyclic forms. Photochromic polymer films with the most acceptable characteristics are obtained from fulgimide-containing oligoaminosiloxane and oligovinyldimethylsilazane. It is found that the photosensitivity of these films is higher than that of similar films based on 1,2-dihetarylethenes.

Masking photochromic films for nanolithography technology

AbstractOne of the problems for modern photolithography is a resolution increase of images recorded on photoresists. For this goal a method of photochromic masking using reversible photochemical transformations of organic systems may be developed. More than 150 photochromic compounds from 11 classes have been studied in solutions and several photochromic compounds exhibiting the best value of the photoindused change of an optical density (ΔOD) at 193 nm have been chosen for the following investigations in the polymer binder and solid films. The method of testing of the photochromic polymer and solid films in operating conditions has been developed. For the testing, a preparation technology of thin photochromic polymer films using the spin‐coating technique has been worked out. It was shown that the polymer and the photochrome should be at an optimal mass ratio in a thin film to reach the maximum of ΔOD. The best result (ΔOD = 0.87) was received for the polymer film based on one of photochromic diarylethenes and poly(methyl)‐methacrylate (at the concentration ratio as 90/10 mass%) of a thickness 450±50 nm under 193 nm laser irradiation at exposure doses about 525 mJ/cm2. An application of these photochromic layers may allow to increase a resolution on the photoresist layer up to 22 nm and more with 193 nm photolithography double‐exposure method. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Grating translation technique as a tool for monitoring phase shifts during holographic recording in azo-polymers

Grating translation technique, elaborated for photorefractive materials, can be used for determination of amplitude and phase grating contributions to light diffraction efficiency after holographic recording in photochromic polymer films. Here, we report application of this technique to in situ analysis of the formation of light inscribed diffraction gratings in azo-functionalized polymers. This technique allows for monitoring amplitudes and phase shifts between phase and amplitude gratings during holographic recording. For the investigation, we chose two azo-polymers with identical azo-substituents and characterized by qualitatively different temporal evolutions of grating build-up process during holographic recording with light s-s polarization geometry. The observed differences in grating recording kinetics for these polymers are explained by the difference in dynamics of build-up of amplitude and phase gratings including surface relief gratings and the spatial phase shifts between them and light interference pattern. Methodology described in this work could be applied to systems in which complex mechanism of refractive index changes upon light illumination are expected.

Photoinduced reorientation processes in thin films of photochromic LC polymers on substrates with a photocontrollable command surface

Orientation and reorientation processes that occur in nematic and cholesteric LC polymer systems under irradiation with plane-polarized light are studied. A copolyacrylate containing phenyl benzoate and azobenzene side groups is synthesized as a nematic polymer; the cholesteric mixture is prepared via doping of the nematic copolymer with the chiral dopant, the derivative of D-isosorbide. Thin layers of the azobenzene-containing photoorientant SD-1 are first used as orienting substrates for polymer liquid crystals. Thin layers of the copolymer and of the mixture are spin-coated on the substrate after irradiation of the photoorientant layer with polarized light. It is shown that after annealing phenyl benzoate and azobenzene side groups of the nematic copolymer orient strictly along the direction of orientation of surface molecules, whereas in the case of the cholesteric mixture, a partial formation of the helical structure is observed. It is demonstrated that all the systems under examination can experience the repeated cyclic reorientation of the cooperative type under irradiation and subsequent annealing of the films.

Light-controlled metal deposition on photochromic polymer films

Fine metal patterning with a small work function is indispensable to the high integration of organic electronics devices including organic light-emitting devices and organic memories. Selective metal deposition on photochromic surfaces is a promising method to prepare such metal patterns. We found that the surface physical properties of polymer films for metal deposition changed depending on their drying temperature and the photoisomerization state of the doped-photochromic diarylethene (DAE). The Mg deposition property on the DAE-doped polystyrene (PS) film was dramatically switched by light irradiation. Light-controlled selective Mg deposition for poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) was also achieved. Fine metal patterning with a width of 15 μm on DAE5%-doped polymer film with maskless vacuum evaporation was successfully demonstrated. Light-controlled selective metal deposition will contribute to the large scale integration of polymer electronics.

Kinetics of Decolorization of Spironaphthooxazine-Doped Photochromic Polymer Films

Photochromic polymeric films were prepared by doping photochromic dye spironaphthooxazine into polymer resin gels such as polyurethane, vinyl copolymer, and copolymer of vinyl and nitorocellulose at different concentrations. All of the composite films show normal photochromism. The kinetics of the photochromism/decoloration in the films were quantified by fitting biexponential equations to their photochromic decay curves after irradiation. It was observed that the decoration process is faster in vinyl copolymer than that in the copolymer of vinyl and nitrocellulose and is the slowest in the case of polyurethane. The decoloration mechanisms of spironaphthooxazine in those polymeric matrixes have been discussed.

Photochromic polymer films based on a 14-F bacteriorhodopsin derivative

Spectral and kinetic characteristics were measured for polymer (gelatin) films based on 14-F bacteriorhodopsin (BR), both wild-type (WT) and D96N mutant, to study the peculiarities of photo-induced transformation of the samples. It was demonstrated earlier that incorporation of 14-F retinal into the apomembrane of both 14-F WT and 14-F D96N produces pigments with drastically different photo-induced behavior, regarding the formation and decay of a red-shifted species at 660 nm. However, similar fundamental differences between 14-F WT and 14-F D96N, if embedded into gelatin matrix, were not observed. Results are discussed in the frame of the relationship between the kinetic rates of two photo-induced processes that occur in suspensions and gelatin films of corresponding pigments. These experimental results can possibly be explained by the difference in kinetics for gelatin films and water suspensions. The main factor in altering the kinetics is the relative humidity of gelatin samples. Therefore, the effect of relative humidity on performance of 14-F BR gelatin films, both WT and D96N, was studied. A range of humidity has been defined for each pigment, in which spectral and kinetic characteristics were changed in the desired direction. It was shown that 14-F WT gelatin films may offer a technological advantage relative to those based on 14-F D96N.

Reversibly Photo-Responsive Polymer Surfaces for Controlled Wettability

Photochromic spiropyran molecules are utilized as additives for the development of polymer surfaces whose wetting characteristics can reversibly respond to irradiation with laser beams of properly chosen photon energy. The hydrophilicity is enhanced upon UV laser irradiation due to the photo-induced isomerization of the non-polar spiropyran molecules to the polar merocyanine. The situation is reversed upon green laser irradiation. Micropatterning of the photochromic-polymer films using soft lithography or photo-polymerization techniques affects their wettability towards a more hydrophobic or more hydrophilic behavior depending on the dimensions of the patterned features and on the hydrophilicity/hydrophobicity of the flat surface. The light-induced wettability variations of the structured surfaces are enhanced by up to a factor of three as compared to those on the flat surfaces. This enhancement is attributed to the photo-induced reversible volume changes to the imprinted gratings, which additionally contribute to the wettability changes due to the light-induced photochromic interconversions.

A new kinetic description of the complex optical behavior in photochromic polymer films

Kinetics of photoinduced birefringence in precolored spirooxazine-doped polymer films pumped with He–Ne laser beams of various powers was investigated in detail. An improved model, elucidating a competition between photo-orientation and photo-isomerization, was precisely presented. Kinetic parameters determined by fitting to the experimental data were analyzed. As He–Ne laser intensity is increased, the thermal rate constants for isomerization and randomization increase in linear and exponential fashions, respectively. Taking these factors into account, the Thermal Effect Model was more suitable for describing the experiment than the Constant Model, indicating that thermal effect of He–Ne laser plays a key role in decreasing the saturated birefringence. According to the Thermal Effect Model, the highest value of the saturated birefringence was obtained at the He–Ne laser power of 6.5 mW in our experiment.

Photomodulated PPV Emission in a Photochromic Polymer Film

We present studies of fluorescence intensity modulation in neat films of a photochromic poly(p-phenylenevinylene) (PPV) derivative. Poly(2-hexyloxy-5-((10-(4-(phenylazo)phenoxy)decyl)oxy)-1,4-phenylenevinylene) (HPA-10-PPV), a PPV derivative functionalized with photoaddressable azobenzene side chains, is known to undergo modulated changes in fluorescence intensity upon azobenzene isomerization in solution. These changes are caused by nonradiative transfer of excitation energy from the PPV backbone to the azobenzene moiety. The efficiency of energy transfer is higher for the cis azobenzene isomer than for trans, a difference that enables fluorescence intensity modulation. Upon film formation, the fluorescence spectra of neat HPA-10-PPV films undergo a red shift of ca. 30 nm compared to those measured in dilute solution. Application of ultraviolet irradiation to induce trans → cis azobenzene isomerization yields a reduction in fluorescence intensity in HPA-10-PPV films that is reversed upon azobenzene cis →...

Multi-States Photochromic Recording and Nondestructive Readout Using IR Light

ABSTRACT A photochromic polymer film containing three different kinds of diarylethene derivatives 1,2-bis(3,5-dimethyl-2-thienyl)perfluorocyclopentene ( 1 ), 1,2-bis(2,5-dimethyl-3-thienyl)-perfluorocyclopentene ( 2 ), and 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene ( 3 ) was prepared. Upon UV irradiation, these three derivatives changed to their closed-ring isomers having different colors, yellow, red, and blue. They showed different spectra not only in UV-vis. region but also in infrared (IR) spectral region. Upon irradiation with visible light of appropriate wavelengths, each closed-ring isomer was selectively bleached, and 3 bits 8 states recording was performed. The 8 states could be read out non-destructively by using IR light of appropriate wavenumbers. The technique will be applicable for near-field IR readout.

Photochromic Cyan Dyes of Fulgide Derivatives in Polymer Film

Abstract Photochromic polymer films doped with 3–4 wt % fulgide derivatives exhibit high thermal and photochemical fatigue resistances as well as good color property to serve as cyan dyes for rewritable color display and printing materials.

Picosecond laser photolysis studies on a photochromic oxidation polymer film consisting of diarylethene molecules

Picosecond laser spectroscopy was applied to the direct detection of photochromic reaction processes in a network polymer film prepared by oxidation polymerization of a diarylethene derivative. Both the coloration due to the cyclization and the decoloration via the cycloreversion took place in less than 30 ps. The time constants of both photochromic reactions were almost the same as those of diarylethene monomers obtained in the solutions, indicating that the oxidation polymer film system retains a similarly high response time as in the solution phase.